The present invention relates to a layered electrophotographic photoconductor comprising an electroconductive support material and a photoconductive double layer which consists of a charge generation layer and a charge transport layer. In particular, it is concerned with a layered electrophotographic photoconductor whose charge generation layer comprises a bisazo pigment selected from the group consisting of the bisazo pigments represented by the general formula (1) and whose charge transport layer contains a charge transport material selected from the group consisting of the anthracene compounds represented by the general formula (2) and distyrylbenzene compounds represented by the general formula (3) ##STR2## wherein A represents --C.sub.6 H.sub.4 --Cl(o), --C.sub.6 H.sub.4 --Cl(m), --C.sub.6 H.sub.4 --Br(o), --C.sub.6 H.sub.4 --Br(m), --C.sub.6 H.sub.4 --F(o), --C.sub.6 H.sub.4 --F(m), --C.sub.6 H.sub.4 --F(p), or --C.sub.6 H.sub.4 --I(m); ##STR3## wherein R.sup.1 represents hydrogen or halogen; and R.sup.2 represents a substituted or unsubstituted phenyl group, a naphthyl group, an anthryl group or a carbazole group, ##STR4## wherein R.sup.3 represents a carbazolyl group, a pyridyl group, a thienyl group, an indolyl group, a furyl group, a phenyl group, a styryl group, a naphthyl group, an anthryl group, which phenyl group, styryl group, naphthyl group and anthryl group are unsubstituted or substituted with one member selected from the group consisting of a dialkylamino group, an alkyl group, an alkoxy group, a carboxyl group or an esterified carboxyl group, halogen, a cyano group, an aralkylamino group, an amino group, a hydroxy group, a nitro group and an acetylamino group.
Conventionally, a variety of inorganic and organic electrophotographic photoconductors are known. As inorganic electrophotographic photoconductors, there are known, for instance, a selenium photoconductor, a selenium-alloy photoconductor, and a zinc oxide photoconductor which is prepared by sensitizing zinc oxide with a sensitizer pigment and dispersing the same in a binder resin. Furthermore, as a representative example of organic electrophotographic photoconductors, an electrophotographic photoconductor comprising a complex of 2,4,7-trinitro-9-fluorenone and poly-N-vinylcarbazole is known.
However, while these electrophotographic photoconductors, have many advantages over other conventional electrophotographic photoconductors, at the same time they have several shortcomings from the viewpoint of practical use.
For instance, a selenium photoconductor which is widely used at present has a shortcoming that its production is difficult and, accordingly, its production cost is high, and is difficult to work into the form of a belt due to its poor flexibility. Furthermore, it is so vulnerable to heat and mechanical shock that it must be handled with the utmost care.
In contrast to this, the zinc oxide photoconductor is inexpensive since it can be produced more easily than the selenium photoconductor. Specifically, it can be produced by simply coating inexpensive zinc oxide particles on a support material. However, it is poor in photosensitivity, surface smoothness, hardness, tensile strength and wear resistance. Therefore, it is not suitable for a photoconductor for use in plain paper copiers in which the photoconductor is used in quick repetition.
The photoconductor employing the aforementioned complex of 2,4,7-trinitro-9-fluorenone and poly-N-vinylcarbazole is also poor in photosensitivity and is therefore not suitable for practical use, particularly for a high speed copying machine.
Recently, extensive studies have been done on the electrophotographic photoconductors of the above-mentioned types, in order to eliminate the above-described shortcomings of the conventional photoconductors. In particular, attention has focused on layered organic electrophotographic photoconductors, each comprising an electroconductive support layer, a charge generation layer comprising an organic pigment formed on the electroconductive support layer, and a charge transport layer comprising a charge transport material formed on the charge generation layer, which are for use in plain paper copiers, since such layered organic electrophotoconductors have high photosensitivity and stable charging properties. As a matter of fact, some types of layered electrophotographic photoconductors are being successfully used in practice. Examples of the layered electrophotographic photoconductors are as follows:
(1) U.S. Pat. No. 3,871,882 discloses a layered electrophotographic photoconductor whose charge generation layer comprises a perylene derivative and whose charge transport layer comprises an oxadiazole derivative.
(2) Japanese Laid-open Patent Applications No. 52-55643 and No. 52-72231 disclose a layered electrophotographic photoconductor whose charge generation layer comprises Chlorodiane Blue which is dispersed in an organic amine and coated on an electroconductive support material and whose charge transfer layer comprises a pyrazoline derivative.
(3) Japanese Laid-open Patent Application No. 53-95033 discloses a layered electrophotographic photoconductor whose charge generation layer comprises a carbozole type bisazo pigment dispersed, for instance, in tetrahydrofuran and coated on an electroconductive support material, and whose charge transport layer comprises 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole or TNF.
(4) Japanese Laid-open Patent Application No. 54-12742 discloses a layered electrophotographic photoconductor of the same type as that disclosed in Japanese Laid-open Patent Application No. 53-95033, in which the carbazole type bisazo pigment is replaced by an oxadiazole type bisazo pigment.
(5) Japanese Laid-open Patent Application No. 54-22834 also discloses a layered electrophotographic photoconductor of the same type as that disclosed in Japanese Laid-open Patent Application No. 53-95033, in which the carbazole type bisazo pigment is replaced by a fluorenone type bisazo pigment.
As mentioned previously, these layered electrophotographic photoconductors have many advantages over other electrophotographic photoconductors, but at the same time, they have a variety of shortcomings.
Specifically, the electrophotographic photoconductor (1) employing a perylene derivative and an oxadiazole derivative presents no problem for use in an ordinary electrophotographic copying machine, but its photosensitivity is insufficient for use in a high speed electrophotographic copying machine. Furthermore, since the perylene derivative, which is a charge generation material and has the function of controlling the spectral sensitivity of the photoconductor, does not necessarily have spectral absorbance in the entire visible region, this photoconductor cannot be employed for use in color copiers.
The electrophotographic photoconductor (2) employing Chlorodiane Blue and a pyrazoline derivative exhibits comparatively good photosensitivity. However, when preparing that photoconductor, an organic amine, for example, ethylene diamine, which is difficult to handle, is necessary as a coating solvent for forming the charge generation layer.
The electrophotographic photoconductors (3) through (5), for which the inventors of the present invention applied for patents, have an advantage over other conventional electrophotographic photoconductors in that the charge generation layers can be prepared easily by coating dispersions of fine pigment particles in an organic solvent (with addition of a binder resin thereto when necessary) on an electroconductive support material. However, the photosensitivities of the photoconductors (3) through (5) are so low that that they cannot be used as photoconductors for high speed electrophotographic copiers.